linux-kernel - Re: IMA policy search speedup

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Message-ID: <20120919200759.GA2169@fieldses.org>
Date:	Wed, 19 Sep 2012 16:07:59 -0400
From:	"J. Bruce Fields" <bfields@...ldses.org>
To:	"Kasatkin, Dmitry" <dmitry.kasatkin@...el.com>
Cc:	James Morris <jmorris@...ei.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-fsdevel@...r.kernel.org,
	linux-security-module <linux-security-module@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Al Viro <viro@...iv.linux.org.uk>,
	Mimi Zohar <zohar@...ux.vnet.ibm.com>
Subject: Re: IMA policy search speedup

On Wed, Sep 19, 2012 at 01:25:26PM +0300, Kasatkin, Dmitry wrote:
> On Wed, Sep 19, 2012 at 7:21 AM, James Morris <jmorris@...ei.org> wrote:
> > On Tue, 18 Sep 2012, Kasatkin, Dmitry wrote:
> >
> >> I looked to <linux/fs.h> and found that there is a possibility to to
> >> add additional flag for sb->s_flags.
> >> For example
> >>
> >> #define MS_NOT_IMA              (1<<25) /* NOT_IMA */
> >> #define IS_I_NOT_IMA(inode)   __IS_FLG(inode, MS_NOT_IMA)
> >>
> >>
> >> Another way is to add additional dedicated integrity related member to
> >> the sb structure.
> >> struct super_block {
> >> ...
> >> #ifdef CONFIG_INTEGRITY
> >>       int s_integrity;
> >> #endif
> >> };
> >>
> >> Obviously there are only few super blocks in the system and few bytes
> >> will not harm.
> >
> > The flag seems better than adding a new struct member.  Why would you need
> > an int for this?
> >
> 
> int is not really needed. It may be char. I just thought that normally
> we have around 10 super blocks
> and it 10 or 40 bytes does not really mater...

Maybe not, but if you use something more generic

	unsigned int s_feature_flags
	#define SF_IMA_ENABLED

then there'd be more uses for that field.

(Two that nfsd would use:
	- does this filesystem support a changeattribute?  (currently a
	  mount flag but that doesn't really make sense in general)
	- is this filesystem case-insensitive?  (whatever that means)
)

--b.

> 
> Actually there is more severe case. IMA cache objects "iint" per inode
> have following members:
>   enum integrity_status ima_status;
>   enum integrity_status evm_status;
> 
> And it is only 5 values per each or 10 values per 8 bytes.
> 8 bytes can be easily replaced by 1 byte.
> 
> Should we improve it?
> 
> >
> >
> > - James
> > --
> > James Morris
> > <jmorris@...ei.org>
> --
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